High-bandwidth data cable standards established by industry standards organizations including the Telecommunications Industry Association (TIA), International Organization for Standardization (ISO), and the American National Standards Institute (ANSI) such as ANSI/TIA-568-C.2, include performance requirements for cables commonly referred to as Category 6A type. These high performance Category 6A cables have strict specifications for maximum return loss and crosstalk, amongst other electrical performance parameters. Failure to meet these requirements means that the cable may not be usable for high data rate communications such as 1000BASE-T (Gigabit Ethernet), 10GBASE-T (10-Gigabit Ethernet), or other future emerging standards.
Crosstalk is the result of electromagnetic interference (EMI) between adjacent pairs of conductors in a cable, whereby signal flow in a first twisted pair of conductors in a multi-pair cable generates an electromagnetic field that is received by a second twisted pair of conductors in the cable and converted back to an electrical signal. Similarly, alien crosstalk is electromagnetic interference between adjacent cables. In typical installations with a large number of cables following parallel paths from switches and routers through cable ladders and trays, many cables with discrete signals may be in close proximity and parallel for long distances, increasing alien crosstalk. Alien crosstalk is frequently measured via two methods: power sum alien near end crosstalk (PSANEXT) is a measurement of interference generated in a test cable by a number of surrounding interfering or “disturbing” cables, typically six, and is measured at the same end of the cable as the interfering transmitter; and power sum alien attenuation to crosstalk ratio, far-end (PSAACRF), which is a ratio of signal attenuation due to resistance and impedance of the conductor pairs, and interference from surrounding disturbing cables.
Return loss is a measurement of a difference between the power of a transmitted signal and the power of the signal reflections caused by variations in impedance of the conductor pairs. Any random or periodic change in impedance in a conductor pair, caused by factors such as the cable manufacturing process, cable termination at the far end, damage due to tight bends during installation, tight plastic cable ties squeezing pairs of conductors together, or spots of moisture within or around the cable, will cause part of a transmitted signal to be reflected back to the source.
Typical methods for addressing alien and internal crosstalk have tradeoffs. For example, alien crosstalk may be reduced by increasing the size of the cable, adding weight and volume and reducing the number of cables that may be placed in a cable tray. Other cables have implemented complex discontinuous EMI barriers and tapes in an attempt to control alien crosstalk and ground current disruption, but add significant expense and may actually increase alien crosstalk in some implementations. Fully shielded cables, such as foil over unshielded twisted pair (F/UTP) designs include drain wires for grounding a conductive foil shield, but are significantly more expensive in total installed cost with the use of shielded connectors and other related hardware. Fully shielded cables are also more difficult to terminate and may induce ground loop currents and noise if improperly terminated.